Tracking Opportunities as a Stakeholder

1. Tracking Opportunities as a Stakeholder

I would like to use the Stakeholder or Additional User as a lookup field (or similar feature) to avoid the extra work of splitting an Opportunity allowing two parties can get credit for a Sale. I should be able to add another Seller as the Stakeholder/Additional User and track their contribution in this manner. Unfortunately I cannot find either Stakeholder or Additional User as any lookup field. Can anyone comment on how I can use this feature to help our Sellers, who often randomly pair up, keep track of the Opps they are losing/winning/retaining? Do you have a better work solution?